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In the United States, HIV could be all but ended within a generation or two if everyone who was at risk of infection took PrEP, a daily preventative medication that the CDC says can can lower the chances of contracting the virus “by more than 90 percent.”

But as encouraging as that figure might be, a depressing new statistic emerged this week in the first study to look at PrEP usage rates using a national probability sample.

Even though PrEP could stop the HIV epidemic in its tracks, only 4.1 percent of sexually active, HIV-negative gay and bisexual men in the United States are taking it.

Most, at least, were familiar with the little blue pill—but still not all: Only about 52 percent of the 18-to-25-year-old cohort, for example, said they knew what PrEP was.

“I wasn’t actually incredibly surprised by that,” said University of California Santa Cruz psychology professor Dr. Phillip Hammack, lead author on the Plos One study, in an interview with The Daily Beast.

Ever since PrEP was approved by the FDA in 2012, public health experts and HIV/AIDS policy advocates have been tracking and studying the challenges in increasing public awareness of the medication.

What was more surprising for Hammack was the fact that a shocking one-quarter of the younger 18-to-25-year-old cohort had never been tested for HIV, as compared to fewer than 8 percent of the men in both the 34-to-41-year-old and 52-to-59-year-old cohorts.

“That was more of a shocker to me than the low PrEP use, I have to say,” Hammack told The Daily Beast.

Those findings combined point to the existence of a too-large number of young gay and bisexual men who don’t know whether they have HIV and aren’t taking an FDA-approved treatment to protect themselves from it.

As co-author Ilan H. Meyer, a public policy scholar at the Williams Institute, noted in the UC Santa Cruz press release on the study, “It is alarming that high-risk populations of men who are sexually actively with same-sex partners are not being tested or taking advantage of treatment advances to prevent the spread of HIV.”

Hammack’s study was borne out of a larger project called the Generations Study being conducted at UCLA’s Williams Institute, an LGBT think tank. In

The goal of Generations, Hammack says, is to look at broader “generational differences in identity, stress, and health” in the LGBT community but he and another investigator “pushed to have us ask questions about PrEP to the men in the study.”

“This was largely influenced by my own professional and personal identity as a gay man of a generation—born in the 1970s—who grew up and came out [during the AIDS crisis],” said Hammack.

Hammack has been thrilled to watch how, over the course of his lifetime, new innovations in treatment and prevention have transformed HIV from a death sentence into a manageable health condition.

But he was curious to know more about how gay and bisexual men were responding to PrEP, given the debates that regularly crop up around its use. Many in the LGBT community believe that PrEP can effectively “eradicate” HIV, as Hammack notes, but some have argued that it will increase sexually risky behaviors and lead to higher rates of other sexually transmitted infections such as chlamydia and gonorrhea.

Taken to an extreme, that latter attitude can have the effect of dissuading men from using PrEP despite its remarkable effectiveness at reducing the risk of HIV infection. Now, thanks to Hammack’s study, the researcher can state that this viewpoint is “thankfully a minority perspective.”

Out of those men in the sample who were familiar with PrEP, over 68 percent expressed a "favorable" attitude toward the medication.

“So, the vast majority, I feel, are really people who should be on it—who probably would be on it—if it weren’t for particular barriers to access,” Hammack told The Daily Beast.

Those barriers to access include a lack of access to LGBT health clinics and affirming physicians outside of urban centers—and also, of course, the cost of the drug itself.

As The Daily Beast has previously reported, PrEP is only currently available in the United States as Truvada, a drug that can cost over $1,000 per month for uninsured Americans.

In response to questions from The Daily Beast at the time, Truvada maker Gilead Sciences referred to its financial assistance program, although LGBT advocates say such a program isn’t adequate to help everyone afford PrEP.

But as Hammack’s study shows, cost PrEP’s price tag can’t account for all of the men who aren’t on it. A simple lack of awareness and conscientiousness, especially among younger men, seems to be a major obstacle in stopping new HIV infections.

For LGBT people living in metropolitan areas, there may be an inflated sense of how widespread PrEP usage has become.

“I was personally surprised,” said Hammack, “just because in the Bay Area, I know a lot of gay men who are on it. However, my personal circle is not necessarily a representative sample.”

That’s why it was important for Hammack and his co-authors to partner with Gallup in order to get a national sample of 470 sexually active gay and bisexual men, ranging in age from 18 to 59 years old.

Indeed, just as troubling as the study’s 4.1 percent figure for overall PrEP use was the fact that one-quarter of the younger 18-to-25 year old cohort had never been tested for HIV, as compared to fewer than 8 percent of the men in both the 34-to-41-year-old and 52-to-59-year-old cohorts.

“That was more of a shocker to me than the low PrEP use, I have to say,” Hammack told The Daily Beast.

Those two findings combined point to the existence of a too-large number of young gay and bisexual men who don’t know whether they have HIV and aren’t taking the only FDA-approved treatment to protect themselves from it.

The generational differences in the study, says Hammack, sadly make sense. Growing up as a gay man during the height of the AIDS epidemic, the researcher says, the thought of going untested would be almost unconscionable.

“When I was young, the only thing that was really visible about gay men at the time was that they die of AIDS,” he told The Daily Beast. “So, coming out and being gay in that era, when I started to become sexually active, it was like, ‘Of course, I’m going to get tested.’ That was part of the culture. You learned it right away as soon as you came out.”

On one hand, Hammack believes that it is of course “a really good thing” that “young men don’t have to worry about dying when they have sex the way that prior generations did.” But he also hopes that they can shake off some of the “complacency” that modern HIV/AIDS treatment advances may have brought along with them.

“It would be good if they recognized that there’s still a very high risk for HIV and it’s really not difficult to prevent transmission,” he said.

The solution, as always, is to make sure more gay and bisexual men know about PrEP.

One encouraging finding from the study itself was that visiting an LGBT health clinic was “associated with PrEP use”—an indication, Hammack says, that the model used by these clinics, which tend to be located in urban centers, is “working and works really well.”

But as more and more LGBT people feel safer living outside of major metropolises like New York and Los Angeles, those clinics can’t reach all the gay and bisexual men who live in more rural or less LGBT-friendly parts of the country.

‘That’s where you don’t necessarily have the level of awareness and sensitivity among physicians and health care providers that you have at an LGBT health clinic,” said Hammack, noting that, anecdotally, some of his friends who live outside of urban centers have asked their doctors about PrEP only to find out that their physicians have never heard of the drug.

“It’s been approved for well over five years, so that’s really troubling,” Hammack said.

What this means, as Hammack and his fellow researchers recommend in the study, is that “public health efforts focused on promoting HIV testing and PrEP awareness need to be more inclusive of diverse populations of gay and bisexual men, especially those in rural areas who are less affiliated with the LGBT community.”

PrEP needs to become known on a national scale, not just among openly gay and bisexual men in big cities.